A liquid crystal display (LCD) device equipped with an area light source apparatus is primarily used for a display monitor of a notebook type personal computer and other various systems because of its structural features such as thin thickness and light weight. Such an LCD device is provided with a rectangular and flat LCD panel to display video images. The LCD panel is connected to narrow, rectangular and flat driver circuits to supply driving signals through a pair of flexible, narrow and flat flexible printed circuits or tape automated bonding (TAB) units.
On the back of the LCD panel the area light source apparatus is provided for irradiating area light to a display region defined in the central portion of the LCD panel. The area light source apparatus is commonly referred to as the backlight. The LCD panel and the backlight provided opposite to it are interposed between, and held by, a bezel and a frame.
The backlight contains a discharge lamp, i.e., a cold cathode tube used for a long, narrow and linear light source and a light guide which is a rectangular and flat plate like area light conversion member. A long side of the light guide is provided opposite to the cold cathode tube to receive linear light from it so that the light guide converts such linear light into an area one by refraction which is projected from a main plane to the LCD panel. The light guide is made of an optically transparent resin material or the like. Prisms are provided on another plane, i.e., the back surface of the light guide.
The cold cathode tube is covered with a curved sheet-like lamp reflector which is in a C-shape in cross section and is provided along the longitudinal axis to reflect the linear light from the cold cathode tube to the incident light side of the light guide. The both edges of the lamp reflector are fixed at those on the front and back surfaces of the light guide, respectively. A rectangular optical sheet is attached to the front surface to make brightness of the light guide uniform and enhanced. A reflection sheet is attached to the back surface of the light guide to reflect light irradiated from the back side of the light guide to its front surface.
The lamp reflector is enlarged to effectively reflect light from the cold cathode tube to a side of the light guide, which is interposed between edge portions of the lamp reflector, as disclosed in Japanese Patent Publication No. 2002-270024, pages 3–5 and FIGS. 3 and 4.
With this structure, however, the light guide interferes with the cold cathode tube or the reflection sheet obstructs an optical path from the lamp reflector when the light guide expands by thermal expansion. Thus, it is necessary to define a gap between another side of the light guide and the frame of the LCD device so that it can prevent the backlight from being uneven or degraded brightness. Nevertheless, repeated thermal expansions make the light guide move and separates from the lamp reflector.